The present invention relates to a switched mode control system with output feedback and under-voltage detection.
Quantum leaps in electronic technology have led to the development of “smart” electrical and electronic products. Each of these products requires a steady and clean source of power from a power supply. In one common power supply known as a switching power supply, an integrated circuit (IC) regulator is connected in series with a primary winding of a transformer to the high voltage direct current (DC) input derived from alternating current (AC) power line through rectification and filtering. Energy is transferred to the secondary winding in a manner controlled by the IC regulator so as to provide a clean and constant output voltage. Another winding called a feedback or bias winding may be used to provide a feedback signal to the IC regulator. Alternately, the feedback signal can come through an opto-coupler from a sense circuit at the secondary output. The feedback signal is used to modulate the duty cycle of the IC regulator or used to allow or disallow cycles in order to control the secondary output.
When the power supply is turned on or off, a temporary uncertainty exists in the output of the power supply. The uncertainty leads to transients or glitches in the output voltage. The condition may cause the output of the power supply to fluctuate unpredictably. For instance, the power supply output may go to zero volts and come back up partially several times during power-down (glitch). Power supplies with auto-restart circuit, which are designed to restart the power supply periodically under fault conditions, are susceptible to such glitches during power-down. Since digital and analog ICs used in modern products are highly sensitive to fluctuations in their voltage supply, such an under-voltage condition may lead to erratic or inoperative products.